Fiber Amplifier is now indispensable to extend the optical signal transmission distance in optical communication field. In this context, RFA (Raman fiber amplifier) and EDFA (erbium-doped fiber amplifier) have already been widely applied in communication systems. With the gradual commercialization of 100 G-CCS (Coherent Communication System), the demand on RFA is increasing. Meanwhile, as the gain medium of RFA is transmission fiber itself with relatively low gain coefficient, it has unique advantage in improving OSNR (Optical Signal Noise Ratio), while it has low price effectiveness in increasing power. On the contrary, compared with RFA, EDFA has larger noise Figure, but is more price-effective in power amplification. Therefore, it can be considered to use them together in the communication system so as to complement and compensate for each other. Nonetheless, the prior art is absent of a unified control platform to regulate the amplification gain and gain coefficient of amplifier, and the current RFA and EDFA are used and adjusted independently, thus it can hardly meet requirements only by using existed RFA and EDFA in combination manner.
Besides, VOA (variable optical attenuator) is embedded in the current EDFA, wherein it keeps the gain on erbium-doped fiber of EDFA unchanged, and the gain change of EDFA is realized by subtracting the attenuation of VOA from the gain on erbium-doped fiber of EDFA, that is, increasing attenuation of attenuation of VOA to reduce EDFA gain, for example, 1 dB reduction of EDFA gain need increasing attenuation of VOA by 1 dB. Consequently, noise Figure of EDFA in small gain is much greater than that in large gain, while pump laser will waste large amount of power due to attenuation of VOA.